WASHINGTON — Some of Hillary Rodham Clinton's biggest backers from New York rallied around Barack Obama Thursday as she signaled her candidacy was ending. The likely Democratic nominee said he won't be hurried into a decision on whether to maker her his running mate.

Clinton, in an e-mail to supporters, said she "will be speaking on Saturday about how together we can rally the party behind Senator Obama. The stakes are too high and the task before us too important to do otherwise."

Aides told NBC News that there would be a private staff event Friday in Washington, followed by the public event on Saturday. They said that she would not waive her right to have her name placed in nomination and that she had not negotiated for anything from Obama, such as debt relief for her campaign.

The e-mail was a shift in tone by the former first lady, who announced 17 months ago that she was "in it to win it." Many of her supporters now are pushing for her to be included as the vice presidential candidate, in their minds a "dream ticket" that would bring Obama her enthusiastic legions and broaden his appeal to white and working-class voters.

But Obama indicated he intends to take his time making a decision.

"We're not going to be rushed into it. I don't think Senator Clinton expects a quick decision and I don't even know that she's necessarily interested in that," Obama told NBC in an interview.

Video: Will Clinton be asked to be VP?
Clinton's move to formally declare that she is backing the Illinois senator came after Democratic congressional colleagues made clear they had no stomach for a protracted intraparty battle. Now that Obama has secured the 2,118 delegates necessary to clinch the nomination, Clinton had little choice but to end her quest, and sooner rather than later.

Some of Clinton's most stolid congressional boosters — other New York lawmakers — were preparing a group endorsement Thursday afternoon of Obama.

A few didn't wait that long. Reps. Gregory Meeks, Edolphus Towns and Yvette Clarke announced late Wednesday they were backing the Illinois senator and calling for party unity.

"We stand firmly in his corner and are ready to help him continue to make history on behalf of the American people," the trio said in a statement.

The move to end her campaign came Tuesday, when Clinton told House Democrats during a private conference call that she would get behind Obama's candidacy and congratulate him for gathering the necessary delegates to be the party's nominee.

Clinton communications director Howard Wolfson said Clinton will express her support for Obama at an event she is hosting Saturday in Washington, D.C., to thank her supporters.

Also in the speech, Clinton will urge once-warring Democrats to focus on the general election and defeating Republican presidential candidate John McCain.

The only degree of uncertainty was how. Clinton is exploring options to retain her delegates and promote her issues, including a signature call for universal health care.

Video: Governors weigh in on VP
The announcement closed an epic five-month nominating battle pitting the first serious female candidate against the most viable black contender ever.

Obama on Tuesday night secured the delegates needed to clinch the Democratic nomination. But Clinton stopped short of acknowledging that milestone, defiantly insisting she was better positioned to defeat McCain in November.

"What does Hillary want? What does she want?" Clinton asked, hours after telling supporters she'd be open to joining Obama as his vice presidential running mate.

But by Wednesday, other Democrats made it abundantly clear they wanted something too: a swift end to the often bitter nominating contest.

Democratic Party Chairman Howard Dean and the Democratic congressional leadership released a statement urging the party to rally behind Obama, and several lawmakers, including Iowa Sen. Tom Harkin, Colorado Sen. Ken Salazar and Louisiana Sen. Mary Landrieu, all endorsed their Illinois colleague.

On the telephone call with impatient congressional supporters that included New York Rep. Charles Rangel, a longtime political patron, Clinton was urged to draw a close to the contentious campaign, or at least express support for Obama.

New York lawmakers wanted to campaign for Obama this weekend, but many weren't comfortable doing that if she hadn't formally endorsed her rival, Rangel said.

"The quicker we proved that we were committed to Senator Obama, then the better for all of us," Rangel said Thursday on CBS' "Early Show."

Rangel said Obama and Clinton need each other — it would help him pick up her supporters if she were on the Democratic ticket, and she "needs to maintain momentum" as a national and international leader.

Her decision to acquiesce caught many in the campaign by surprise and left the campaign scrambling to finalize the logistics and specifics behind her campaign departure.

It was an inauspicious end for a candidacy that appeared all but indestructible when it began Jan. 20, 2007.

Armed with celebrity, a prodigious fundraising network, a battle-tested campaign team and husband who also was a popular two-term former president, Clinton was believed by many observers to be unbeatable.

But in Obama, the New York senator faced an opponent who appeared perfectly suited to the time — a charismatic newcomer who had opposed the Iraq war from the beginning — in contrast to her — and who offered voters a compelling message of change. Clinton voted for the legislation that authorized military force against Iraq, a decision that hampered her campaign from the beginning.

Information from NBC News, The Associated Press, The New York Times and The Wall Street Journal contributed to this report.